Determination of the yield strength and the energy distribution in the milling of Inconel 718 considering fracture toughness

This article presents an analytical method to determine the yield strength and the energy distribution in the milling process of nickel alloy Inconel 718 by incorporating the fracture toughness, the plastic deformation and the friction effect. To study the geometry and mechanics in the oblique cutting process, mathematical analyses are done to derive the angles related to the friction (λ, λ_n), the shear flow (δ, ϕ_n) and the chip flow (β). Geometrical model for the serrated chip formation is established to derive the equations that are needed for calculating the fundamental quantities such as forces, velocities and shear strains. Then, the workpiece material's cutting yield strength and fracture toughness are predicted, and efforts also focus on characterizing and classifying the geometrical relationships among the uncut chip thickness, the actual feed rate and the instantaneous radial depth of cut. Equations to calculate the work in relation to the plastic flow, friction and material fracture are established, and subsequently, energy distribution for the serrated chip formation is evaluated from the cutting data. The proposed method has the advantages of convenience, feasibility and generality, compared with the standard tensile tests and the standard fracture mechanical tests, which are usually used to measure the material properties under static loadings or at a range of temperatures and loading rates. A series of milling tests have verified the method.